Faceted navigation, such as filtering by color or price range, can be helpful for your visitors, but it’s often not search-friendly since it creates many combinations of URLs with duplicative content. With duplicative URLs, search engines may not crawl new or updated unique content as quickly, and/or they may not index a page accurately because indexing signals are diluted between the duplicate versions. To reduce these issues and help faceted navigation sites become as search-friendly as possible, we’d like to:

In an ideal state, unique content -- whether an individual product/article or a category of products/articles -- would have only one accessible URL. This URL would have a clear click path, or route to the content from within the site, accessible by clicking from the homepage or a category page.

Ideal for searchers and Google Search

Clear path that reaches all individual product/article pages

On the left is potential user navigation on the site (i.e., the click path), on the right are the pages accessed.

One representative URL for category pagehttp://www.example.com/category.php?category=gummy-candies

While humans may be able to decode odd URL parameters, such as “,,”, crawlers have difficulty interpreting URL parameters when they’re implemented in a non-standard fashion. Software engineer on Google’s Crawling Team, Mehmet Aktuna, says “Using non-standard encoding is just asking for trouble.” Instead, connect key=value pairs with an equal sign (=) and append multiple parameters with an ampersand (&).

Worst practice #2: Using directories or file paths rather than parameters to list values that don’t change page content.

Worst practice:

example.com/c123/s789/product?swedish-fish (where /c123/ is a category, /s789/ is a sessionID that doesn’t change page content)

Good practice:

example.com/gummy-candy/product?item=swedish-fish&sid=789 (the directory, /gummy-candy/,changes the page content in a meaningful way)

Best practice:

example.com/product?item=swedish-fish&category=gummy-candy&sid=789 (URL parameters allow more flexibility for search engines to determine how to crawl efficiently)

It’s difficult for automated programs, like search engine crawlers, to differentiate useful values (e.g., “gummy-candy”) from the useless ones (e.g., “sessionID”) when values are placed directly in the path. On the other hand, URL parameters provide flexibility for search engines to quickly test and determine when a given value doesn’t require the crawler access all variations.

Common values that don’t change page content and should be listed as URL parameters include:

Session IDs

Tracking IDs

Referrer IDs

Timestamp

Worst practice #3: Converting user-generated values into (possibly infinite) URL parameters that are crawlable and indexable, but not useful in search results.

Rather than allow user-generated values to create crawlable URLs -- which leads to infinite possibilities with very little value to searchers -- perhaps publish category pages for the most popular values, then include additional information so the page provides more value than an ordinary search results page. Alternatively, consider placing user-generated values in a separate directory and then robots.txt disallow crawling of that directory.

Extraneous URL parameters only increase duplication, causing less efficient crawling and indexing. Therefore, consider stripping unnecessary URL parameters and performing your site’s “internal housekeeping” before generating the URL. If many parameters are required for the user session, perhaps hide the information in a cookie rather than continually append values like cat=gummy-candy&cat=lollipops&cat=gummy-candy& ...

Worst practice #5: Offering further refinement (filtering) when there are zero results.

Worst practice:

Allowing users to select filters when zero items exist for the refinement.

Refinement to a page with zero results (e.g., price=over-10) is allowed even though it frustrates users and causes unnecessary issues for search engines.

Best practice

Only create links/URLs when it’s a valid user-selection (items exist). With zero items, grey out filtering options. To further improve usability, consider adding item counts next to each filter.

Refinement to a page with zero results (e.g., price=over-10) isn’t allowed, preventing users from making an unnecessary click and search engine crawlers from accessing a non-useful page.

Prevent useless URLs and minimize the crawl space by only creating URLs when products exist. This helps users to stay engaged on your site (fewer clicks on the back button when no products exist), and helps minimize potential URLs known to crawlers. Furthermore, if a page isn’t just temporarily out-of-stock, but is unlikely to ever contain useful content, consider returning a 404 status code. With the 404 response, you can include a helpful message to users with more navigation options or a search box to find related products.

Best practices for new faceted navigation implementations or redesigns

New sites that are considering implementing faceted navigation have several options to optimize the “crawl space” (the totality of URLs on your site known to Googlebot) for unique content pages, reduce crawling of duplicative pages, and consolidate indexing signals.

Determine which URL parameters are required for search engines to crawl every individual content page (i.e., determine what parameters are required to create at least one click-path to each item). Required parameters may include item-id, category-id, page, etc.

Determine which parameters would be valuable to searchers and their queries, and which would likely only cause duplication with unnecessary crawling or indexing. In the candy store example, I may find the URL parameter “taste” to be valuable to searchers for queries like [sour gummy candies] which could show the result example.com/category.php?category=gummy-candies&taste=sour. However, I may consider the parameter “price” to only cause duplication, such as category=gummy-candies&taste=sour&price=over-10. Other common examples:

Consider implementing one of several configuration options for URLs that contain unnecessary parameters. Just make sure that the unnecessary URL parameters are never required in a crawler or user’s click path to reach each individual product!

Option 1: rel="nofollow" internal links

Make all unnecessary URLs links rel=“nofollow.” This option minimizes the crawler’s discovery of unnecessary URLs and therefore reduces the potentially explosive crawl space (URLs known to the crawler) that can occur with faceted navigation. rel=”nofollow” doesn’t prevent the unnecessary URLs from being crawled (only a robots.txt disallow prevents crawling). By allowing them to be crawled, however, you can consolidate indexing signals from the unnecessary URLs with a searcher-valuable URL by adding rel=”canonical” from the unnecessary URL to a superset URL (e.g. example.com/category.php?category=gummy-candies&taste=sour&price=5-10 can specify a rel=”canonical” to the superset sour gummy candies view-all page at example.com/category.php?category=gummy-candies&taste=sour&page=all).

Option 2: Robots.txt disallow

For URLs with unnecessary parameters, include a /filtering/directory that will be robots.txt disallow’d. This lets all search engines freely crawl good content, but will prevent crawling of the unwanted URLs. For instance, if my valuable parameters were item, category, and taste, and my unnecessary parameters were session-id and price. I may have the URL:example.com/category.php?category=gummy-candies
which could link to another URL valuable parameter such as taste:example.com/category.php?category=gummy-candies&taste=sour.
but for the unnecessary parameters, such as price, the URL includes a predefined directory, /filtering/:example.com/filtering/category.php?category=gummy-candies&price=5-10
which is then robots.txt disallowed

User-agent: *Disallow: /filtering/

Option 3: Separate hosts

If you’re not using a CDN (sites using CDNs don’t have this flexibility easily available in Webmaster Tools), consider placing any URLs with unnecessary parameters on a separate host -- for example, creating main host www.example.com and secondary host, www2.example.com. On the secondary host (www2), set the Crawl rate in Webmaster Tools to “low” while keeping the main host’s crawl rate as high as possible. This would allow for more full crawling of the main host URLs and reduces Googlebot’s focus on your unnecessary URLs.

Be sure there remains at least one click path to all items on the main host.

If you’d like to consolidate indexing signals, consider adding rel=”canonical” from the secondary host to a superset URL on the main host (e.g. www2.example.com/category.php?category=gummy-candies&taste=sour&price=5-10 may specify a rel=”canonical” to the superset “sour gummy candies” view-all page, www.example.com/category.php?category=gummy-candies&taste=sour&page=all).

Prevent clickable links when no products exist for the category/filter.

Help the searcher experience by keeping a consistent parameter order based on searcher-valuable parameters listed first (as the URL may be visible in search results) and searcher-irrelevant parameters last (e.g., session ID).

Improve indexing of individual content pages with rel=”canonical” to the preferred version of a page. rel=”canonical” can be used across hostnames or domains.

Improve indexing of paginated content (such as page=1 and page=2 of the category “gummy candies”) by either:

Adding rel=”canonical” from individual component pages in the series to the category’s “view-all” page (e.g. page=1, page=2, and page=3 of “gummy candies” with rel=”canonical” to category=gummy-candies&page=all) while making sure that it’s still a good searcher experience (e.g., the page loads quickly).

Be sure that if using JavaScript to dynamically sort/filter/hide content without updating the URL, there still exists URLs on your site that searchers would find valuable, such as main category and product pages that can be crawled and indexed. For instance, avoid using only the homepage (i.e., one URL) for your entire site with JavaScript to dynamically change content with user navigation -- this would unfortunately provide searchers with only one URL to reach all of your content. Also, check that performance isn’t negatively affected with dynamic filtering, as this could undermine the user experience.

Best practices for existing sites with faceted navigation

First, know that the best practices listed above (e.g., rel=”nofollow” for unnecessary URLs) still apply if/when you’re able to implement a larger redesign. Otherwise, with existing faceted navigation, it’s likely that a large crawl space was already discovered by search engines. Therefore, focus on reducing further growth of unnecessary pages crawled by Googlebot and consolidating indexing signals.

Use parameters (when possible) with standard encoding and key=value pairs.

Verify that values that don’t change page content, such as session IDs, are implemented as standard key=value pairs, not directories

Prevent clickable anchors when products exist for the category/filter (i.e., don’t allow clicks or URLs to be created when no items exist for the filter)

Help the searcher experience by keeping a consistent parameter order based on searcher-valuable parameters listed first (as the URL may be visible in search results) and searcher-irrelevant parameters last (e.g., avoid example.com/category?session-id=123&tracking-id=456&category=gummy-candies&taste=sour& in favor of example.com/category.php?category=gummy-candies&taste=sour&session-id=123&tracking-id=456)

Configure Webmaster Tools URL Parameters if you have strong understanding of the URL parameter behavior on your site (make sure that there is still a clear click path to each individual item/article). For instance, with URL Parameters in Webmaster Tools, you can list the parameter name, the parameters effect on the page content, and how you’d like Googlebot to crawl URLs containing the parameter.

URL Parameters in Webmaster Tools allows the site owner to provide information about the site’s parameters and recommendations for Googlebot’s behavior.

Be sure that if using JavaScript to dynamically sort/filter/hide content without updating the URL, there still exists URLs on your site that searchers would find valuable, such as main category and product pages that can be crawled and indexed. For instance, avoid using only the homepage (i.e., one URL) for your entire site with JavaScript to dynamically change content with user navigation -- this would unfortunately provide searchers with only one URL to reach all of your content. Also, check that performance isn’t negatively affected with dynamic filtering, as this could undermine the user experience.

Improve indexing of individual content pages with rel=”canonical” to the preferred version of a page. rel=”canonical” can be used across hostnames or domains.

Improve indexing of paginated content (such as page=1 and page=2 of the category “gummy candies”) by either:

Adding rel=”canonical” from individual component pages in the series to the category’s “view-all” page (e.g. page=1, page=2, and page=3 of “gummy candies” with rel=”canonical” to category=gummy-candies&page=all) while making sure that it’s still a good searcher experience (e.g., the page loads quickly).